[英]C++: vector in struct, push_back error
I am trying to save the data in a vector in structs. 我试图将数据保存在结构中的向量中。 Since I do not know the length of each data, I used
push_back
. 由于我不知道每个数据的长度,我使用了
push_back
。 However, the for loop
does not work and I got Command terminated
after the first i
loop. 但是,
for loop
不起作用,我在第一个i
循环后Command terminated
了Command terminated
。
I tried several answers like this , but none of them works. 我试了好几种答案像这样 ,但他们没有工作。
Here is a simplified version of what I tried (and gives the same error): 这是我尝试的简化版本(并给出相同的错误):
#include <iostream>
#include <vector>
using namespace std;
typedef struct{
vector<int> words;
}DATA_STRUCT;
void add(DATA_STRUCT *data){
for(int i=0; i<5; i++){
for(int s=0;s<3; s++){
(&data)[i] -> words.push_back(s);
cout << i << s << endl;
}
}
}
int main(){
DATA_STRUCT *data = new DATA_STRUCT[5];
add(data);
cout << (&data)[0] -> words[0] << endl;
}
The problem lies with: 问题在于:
(&data)[i] -> words.push_back(s);
&data
evaluates to a DATA_STRUCT **data
. &data
计算为DATA_STRUCT **data
。 By using (&data)[i]
, you are accessing memory that you are not supposed to, which causes undefined behavior. 通过使用
(&data)[i]
,您正在访问您不应该访问的内存,这会导致未定义的行为。
That line can be a lot simpler. 这条线可以简单得多。
data[i].words.push_back(s);
You are almost there. 你快到了。 Here is the correct approach :-
这是正确的方法: -
#include <iostream>
#include <vector>
using namespace std;
typedef struct{
vector<int> words;
}DATA_STRUCT;
void add(DATA_STRUCT *data){
for(int i=0; i<5; i++){
for(int s=0;s<3; s++){
data[i].words.push_back(s); //<-- edit
cout << i << s << endl;
}
}
}
int main(){
DATA_STRUCT *data = new DATA_STRUCT[5];
add(data);
cout << data[0].words[0] << endl; //<-- edit
delete[] data; //Thank juanchopanz
}
&data
is wrong, you want the value. &data
错误,你想要的价值。
data[xxx]
works like the "get value" operation. data[xxx]
作用类似于“获取值”操作。 (roughly speaking) (粗略地说)
There is also memory leak at :- 还有内存泄漏: -
DATA_STRUCT *data = new DATA_STRUCT[5];
It is new without delete , so I also add delete[] data;
它是新的没有删除 ,所以我还添加了
delete[] data;
. 。 (Thank juanchopanza )
(感谢juanchopanza )
To answer Tom de Geus :- 要回答Tom de Geus : -
Any way to avoid the new here?
有什么办法可以避免这里新的?
Here is the better version :- 这是更好的版本: -
DATA_STRUCT data[5];
add(data);
cout << data[0].words[0] << endl;
To answer additional question from OP :- 要回答OP的其他问题: -
Why can we use arrow instead of dot?
为什么我们可以使用箭头代替点? Is data in the add function a struct of pointer?
add函数中的数据是指针的结构吗?
data
is DATA_STRUCT*
data
是DATA_STRUCT*
(&data)
is DATA_STRUCT**
(&data)
是DATA_STRUCT**
(&data)[i]
is DATA_STRUCT*
(&data)[i]
是DATA_STRUCT*
(&data)[i]->
is DATA_STRUCT
(&data)[i]->
是DATA_STRUCT
(&data)[i]->words
is DATA_STRUCT::words
(&data)[i]->words
是DATA_STRUCT::words
It is a wrong address, but in term of (only) syntax, it is correct. 这是一个错误的地址,但就(仅)语法而言,它是正确的。
Wrong address ~ undefined behavior = can work OK / work but wrong / crash 错误的地址〜未定义的行为=可以正常工作/工作但错误/崩溃
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